In semiconductor manufacturing industry, new materials with low dielectric constants (known in the art as “low-k dielectrics”) are being investigated for their potential use as insulators in semiconductor chip designs. A low dielectric constant material aids in enabling further reductions in integrated circuit feature dimensions. Damascene interconnect features are advantageously used to provide planarized interconnect structures that afford the use of multiple interconnect layers and therefore increase levels of device integration. There is a trend in the semiconductor industry towards the use of low-k dielectric materials, particularly used in conjunction with copper conductive lines, to reduce the RC time delay of the conductive lines. Some low-k dielectric materials are porous and/or etch very quickly, and it is difficult to adequately control the etch process, particularly in a dual damascene structure and process.
Various materials appear to be suitable for use with the damascene deposited interconnect lines, such as an ultra low-k dielectric material. However the low-k dielectric material creates problems, for example, its higher sensitivity to etchant used in formation of integrated circuit structures. This results in damage to such low-k material during the etching of openings therein for formation of vias and trenches. The etching damage can cause an increased effective dielectric constant (keff), degradation of the dielectric properties of the inter-metal dielectric layer, a high resistance of metal line, and disconnection (open) of copper line. One approach to solving the problems is to expose the etched surfaces (e.g., sidewall surfaces of etched via and trench of the low-k dielectric layer) to plasma formed from H2 gas. This method reduces damage to the low-k dielectric layer, but disadvantageously induces higher k value due to extra ion bombardment.
Therefore, it is desirable to provide a method of eliminating etching damage to a low-k dielectric layer in a damascene structure for making the low-k dielectric layer with improved structural properties without compromising or deteriorating its electrical properties.